A mechanically or electromechanically driven compass watch is already known, as described for example in the patent application FR 2 203 106, including time indicating elements such as hours and minutes hands respectively which are associated with direction indicating means constituted by a compass card.
Such compass card which enables one thus to be oriented through indicating the position of the different cardinal points, is kinematically coupled to a horometric movement which, in a standard manner, controls the displacement of the hours and minutes hands and which, at each instant, orients the compass card in a manner such that the south inscribed on the latter points in the direction corresponding to the bisector of the acute angle which is formed between the hours hand and midday marked on the watch. As is well understood, in order to determine validly the south direction and, consequently, that of the other cardinal points, it is indispensable, during the reading, to point the hours hand simultaneously towards the sun.
Further, there is known in particular according to patent application DE 3 631 513, a compass watch which is provided, in addition to the two standard hours and minutes hands, with a third hand referred to as the solar hand, which effects one revolution around the dial every 24 hours under the action of the horometric movement which controls it and which forms the indicating means to be pointed towards the sun.
Thus, in order to determine one's orientation, it suffices to point such solar hand towards the sun, then to read from the watch the direction indications, namely to take note of the information given by the different cardinal points which are permanently marked on the watch, and in particular on the dial thereof.
These two watch types thus enable one to be oriented very rapidly in avoiding utilization of a magnetized hand which, as is known, is particularly sensitive to any exterior influence. Moreover such magnetized hand may be disturbed in a non-negligible manner by stray fields which may be created by the watch itself.
Nevertheless, these two types of compass watch driven mechanically or electromechanically, may furnish substantial orientation errors, essentially by reason of the gap between the legal or local time of day indicated by the watch and true solar time which in fact is that which alone should be taken into account since the orientation is given to the user as a function of his position relative to the sun.
This gap between the legal or local time of day and the true solar time may be substantial and bring about errors on the order of several degrees.
Effectively, on the one hand, it is known that true solar time coincides with the legal or local time of day only for persons located exactly on one of the meridians (that of Greenwich for Western Europe) All geographic separation relative to this meridian brings about a subsequent gap between the two times of day respectively legal and true solar, and gives a totally imprecise reading.
On the other hand, whether in winter or eventually summer, our ega time absolutely does not coincide with true solar time, the gaps varying from one to two hours.
It is evident that a correction method could consist in readjusting permanently, that is to say, at each measurement, the time displayed on the watch; in other words, to replace the legal time of day by true solar time and inversely.
However, such a manipulation may bring about errors if the user, after several readings and several resettings of the legal time of day, no longer remembers exactly on which time legal or solar, he has stopped.
In addition, such manipulations necessitate the decoupling of the drive of the horometric movement relative to the hands, which brings about, inevitably, loss of the correct time.
Thus, the invention has as its purpose to answer to these difficulties through proposal of a compass watch capable of being freed from the seasonal variations of time, geographical displacements relative to the meridians enabling reference to the legal time of day and spreads caused by the equation of time and this in order to assure to the user an excellent precision at the time of his orientation.
The invention also has as its purpose to provide a compass watch responding to the problem mentioned hereinabove and the structure of which enables one easily to call on a standard horometric movement without costly adaptation thereof.